According to a manufacturing method of an insert molded article by placing in a molding die a metallic part as an insert with a thermoset resin adhesive applied to a joining surface relative to plastic and injecting a molten plastic material from a gate into the molding die, when the injection molding is performed with the adhesive in an uncured state, the adhesive is swept away by the molten plastic material injected into the molding die, thereby reducing the strength of adhesion between the metallic part and the plastic (for example, refer to Patent Document 1, paragraph [0010]).
In addition, when the injection molding is performed with the adhesive in a fully cured state, the adhesive and the plastic do not conform well to each other to reduce the strength of adhesion between the metallic part and the plastic (for example, refer to Patent Document 1, paragraph [0010]).
To solve the foregoing problems and improve the strength of adhesion between the metallic part and the plastic, there has been proposed a method for performing injection molding with the adhesive in a semi-cured state (for example, Patent Document 1, claim 1, and paragraphs [0008] and [0011]).
Such a technique of performing injection molding after bringing a thermoset resin adhesive to be applied to the insert into a semi-cured state is also used for a manufacturing method of a magnetic encoder used to detect the number of rotations of a rotating body (for example, Patent Documents 2 and 3).
The “semi-cured state” is regarded to mean that the adhesive is not fully cured but has caused curing reaction to some degree (refer to Patent Document 2, paragraph [0046], and Patent Document 3, paragraph [0025]), and would not be flown out by the high-pressure molten plastic material injected from a gate into the molding die at the time of insert molding (for example, refer to Patent Document 1, paragraph [0011], Patent Document 2, paragraph [0043], and Patent Document 3, paragraph [0019]).
It is known that, in the technique of bringing the thermoset resin adhesive into a semi-cured state to adhere to both the metallic part and the plastic, it is not easy to hold the adhesive in the semi-cured state, and the semi-cured adhesive is unstable and causes large fluctuations in the strength of adhesion between the metallic part and the plastic with insufficient reproducibility (for example, refer to Patent Document 1, paragraph [0012]).
There is also well known a bearing device that includes a rotation speed detection device using the magnetic encoder in a rolling bearing (hub bearing) for automobile wheel support (for example, Patent Document 2, FIG. 1, and Patent Document 3, FIG. 1).
The bearing device is intended to support automobile wheels to be used in various environments. The magnetic encoder may be exposed to heavy weather conditions such as wind and snow, wind and rain, the hot sun, and the like, and may be used at about −40 to 120° C. with large temperature changes. In addition, the magnetic encoder may be encrusted with a snow melting agent including calcium chloride as a main ingredient or a highly aggressive oil or the like. These stresses are known to cause reduction in the adhesiveness of the magnetic encoder.